Solid compound of rhodium and tungsten and manufacturing process therefor

ABSTRACT

RH2WO6 CRYSTALLIZED IN THE TETRAGONAL SYSTEM UNDER THE RIRUTILE FORM, THE PARAMETERS AO AND CO BEING 4.609 AND 9.083 A. RESPECTIVELY, HAVING AN ELECTRICAL CONDUCTIVITY OF 10-4 (OHM.CM)-1 AND ENERGY GAP OF 0.03 E.V.

United States Patent Int. Cl. C01g 41/00, 55/00; H01b N08 US. Cl. 2s2- s1s 3 Claims ABSTRACT OF THE DISCLOSURE Rh WO crystallized in the tetragonal system under the trirutile form, the parameters a and s being 4.609 and 9.083 A. respectively, having an electrical conductivity of (ohm-cm.)- and energy gap of 0.03 e.v.

BACKGROUND OF THE INVENTION The present invention relates to a new oxygen-containing compound of rhodium and tungsten, Rh -WO and to a manufacturing process therefor.

SUMMARY OF THE INVENTION The present invention concerns a compound Rh WO- DESCRIPTION OF THE PREFERRED EMBODIMENTS The new compound was prepared from powdered and W0 which were mixed in equimolecular quantities, then comminuted and pelletized.

The starting oxide Rh O was obtained by pyrolysis at 500 C. of pure rhodium nitrate supplied by Fluka, whereas the WO was a product supplied by UCB, chemical analysis grade.

In an example, 2.32 g. of the W0 and 2.54 g. of the resultant Rh O were mixed together. Then during a period of 1 hour, the mixture was comminuted dry in a steel ball mill lined with tungsten carbide and provided with tungsten carbide balls in order to obtain a well homogenized mixture which was then pelletized in the shape of a disc at room temperature under a pressure of 1000 kg./cm. (6.35 tons per square inch) and heated in air at 950 C., for 24 hours.

The resultant black porous disc of Rh WO' was then comminuted in the aforesaid ball mill until all particles had a particle size of one micron or below.

An X-ray crystallographic analysis carried out on the thus obtained powder showed that the Rh WO crystallizes in the tetragonal system and belongs to the trirutile type. The unit cell has the following parameters:

a =4.609 A. and c -=9.083 A.

The unit cell contains two molecules of Rh WO The intensities of the lines and the observed interplanar 3,735,270 Patented May 29, 1973 ice spacings determined in the X-ray crystallographic analysis are given in the following table.

Interplanar spacing d (A.) RhzWOe The X-ray crystallographic data show that the thermal treatment of the starting oxides is sufiicient to obtain a complete loss of identity of the starting oxides with complete conversion to pure Rh WO in a good crystalline state.

In order to measure the electrical conductivity of the obtained Rh WO the powder resulting from comminuting the porous disc was again pelletized under the same conditions used for pelletizing the Rh O -WO mixture. The measured electrical conductivity was in the range of 10 (ohm-cm.)" The obtained Rh WO' is thus really a semiconductor and its forbidden gap, or energy gap, amounts to 0.03 e.v. The terms forbidden gap and energy gap refer to the distance between the top of the valence band and the bottom of the conduction band; these terms appear, for instance, in Physics and Technology of Semiconductor Devices by A. S. Grove, pages 91-95 and 102.

The manufacturing process for the compound of the present invention is very easy and the operative conditions are easily reproducible.

Used as an anodic operative surface in the electrolysis of sodium chloride, the new compound presents very interesting polarization properties and is very resistant to electrochemical attack under cellconditions.

On account of its properties, the compound Rh /WO of the present invention is very useful for industrial applications not only as an electrode in various electrochemical processes, but also as an oxidation catalyst in organic chemistry or as a component in composite semiconductive devices.

The starting materials were obtained from Fluka, CH- 9470 Buchs (Switzerland) and UCB, 33 rue dAnderlecht, 1620 Drogenbos (Belgium).

The trademark designation of the rhodium nitrate was rhodium (III) -nitrat Dihydrat purissimum No. 83,760. The trademark designation of the W0 was anhydride tungstique pour analyse No. 1925. The rhodium nitrate was supplied in a purity grade designated as purissimum which meant a chemical analysis in weight-percent as follows:

the W was supplied in a purity grade designated as: chemical analysis which meant a chemical analysis in weight-percent as follows:

lPercent Insoluble in diluted NaOH Max. 0.03

Chlorides Max. 0.0015 Heavy metals (-Pb) Max. 0.002 Iron (Fe) Max. 0.004 Molybden (Mo) Max. 0.05 Ammonium (NH Max. 0.0015 Arsenic (As) Max. 0.0015 W0 Balance The chemical analysis of the resultant Rh WO was in Weight-percent as follows:

Percent Rh 42.4 W 37.9 0 Balance The X-ray crystallographic data of the table were obtained by irradiating the comminuted product with a beam of Cu Ku radiation. The intensity designations are according to the ASTM system as follows:

Designation in table AST M (relative intensity) 100 I/I Demonstrating the utility of the Rh WO of the present invention for carrying out the half reaction 2Cl -Cl +2e is the following example. The comminuted product was spread on a titanium plate and subjected to a pressure of 1000 kgJcm. at a temperature of 475 C. for 20 minutes to provide a. coating of 5 grams/m. of titanium surface. The coating side of the titanium plate was then subjected, as anode, to two different tests: the first one to measure the overvoltage for the liberation of chlorine under a given anodic current density ka./m. the second one to determine the wear or consumption of noble metal as related to the quantity of evolved chlorine. The term overvoltage is used herein in the same since as it is used at pages 48 8-492 of Physical Chemistry by Walter J. Moore, Prentice-Hall Inc., second edition. In the overvoltage test the coated plate was used as anode for the electrolysis of a brine containing 250 g. NaCl/ kg. of solution saturated with chlorine at 60 C. and at an approximate pH of 2. Under these conditions, the coated plate of this example showed an overvoltage in the range 250 mv. under an anodic current density of 10 kajmfi. In the wear test, the coated plate was used as anode in a cell with a flowing mercury cathode for the electrolysis of a brine saturated with sodium chloride and chlorine, between and C., under a constant anode-cathode potential difference, the test being stopped when the current density was reduced to one half of its initial value (initial value generally was between 30 and 40 ka./m. Under these conditions, the tested plate produced 9 tons of chlorine per square meter of active surface; the rhodium consumption lay below 200 mg. per ton of chlorine produced under an average current density of 20 ka./m.

After the 2.32 g. of W0 and 2.54 g. of Rh O have been comminuted, the Well homogenized mixture has a particle size distribution lower than Lu.

The pelletizing is carried out without any binding additive.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended Within the meaning and range of equivalents of the appended claims.

We claim:

1. Rh WO crystallized in the tetragonal system under the trirutile form, the parameters a and c being 4.609 and 9.083 A. respectively, having an electrical conductivity of 10- (ohm-cm.) and an energy gap of 0.03 erv.

2. Rh WO as claimed in claim 1 and having line intensities and interplanar spacing as follows:

Interplanar spacin d (A.

Miller indices Intensity Nwwomrowwwwwmwwwc b aov oczm-n-nowoowco Ft awome-owmwweeoceowm H UNITED STATES PATENTS 3,294,701 12/1966 Vogel et al 423606 CHARLES E. VAN HORN, Primary Examiner US. Cl. X.R. 423592, 606 

